It is estimated that over the last hundred years damage from earthquakes has averaged from 2-4 billion a year in the United States. Damage from floods annually yearly costs a similar amount in the United States. Earthquake events tend to happen less frequently than flood events. However, the damage costs for any significant event tend to be quite large. World-wide, the costs in lives and physical damage are much greater.
In the U.S., Earthquake risk is primarily focused on the West Coast. However, the new Madrid fault system where Illinois, Kentucky, Tennessee, Missouri and Arkansas come together along the upper Mississippi river also has the potential for generating a large earthquake. Flood damage can occur nearly anywhere in the U.S.
Away from coastal regions, flooding primarily is caused from overflowing of rivers and their associated tributaries. On the coasts, which have the highest population density (half of the US population lives within 50 miles of the coast), flooding is caused from overflowing rivers, storm surges and tidal surges. It is expected global warming and an associated rises in sea level and weather variability will only exacerbate coastal flooding and inland flooding issues. In addition, the West coast, Hawaii and Alaska face a significant flooding threat from Tsunamis and associated earthquakes. It is estimated the repair of the damage from recent earthquake and tsunami in Japan in 2011 will cost on the order of $300 billion dollars.
Cost effective methods for mitigating flood and earthquake damage are limited. For floods, one method is to determine flood prone regions and avoid building in these areas. Flood maps often affect the availability and pricing of land and insurance in the areas covered by the maps. Another method for flood mitigation is to raise the building. Essentially, a multi-story building is constructed where the lower level remains unused, which is inefficient. This method is sometimes applied to smaller buildings, such as houses, but is not generally applied to medium or larger sized buildings. Further, the construction is usually not sufficient to withstand powerful flood conditions.
Levees are used to control floods. However, levees are expensive to build and maintain, have a high-environmental impact, utilize a lot of land and, in areas with earthquake risks, are vulnerable to collapse in an earthquake. Further, as past experience has shown, levees are vulnerable to point failures where a breach at just one location can mitigate most of the benefits of building the levee in the first place.
For seismic activity, earthquake maps guide building practices and in some instances may identify areas subject to soil liquefaction which are unsuitable for building. To mitigate seismic damage, larger buildings, such as skyscrapers, sometimes use base isolation and/or vibration dampening systems to mitigate earthquake damage. Medium and smaller size building use building techniques and/or are retrofitted with strengthening mechanisms which prevent catastrophic failure and subsequent loss of life but still subject the building to significant damage in an earthquake. Base isolation is generally not considered cost effective for medium and smaller size building and is rarely applied.
In view of the above, improved and cost-effective methods and apparatus for constructing buildings which mitigate seismic and flood damage are needed.